1. Field of the Invention
The present invention relates to an adjusting device and method for adjusting the relative positioning of planar, generally transparent components, such as liquid crystal plates.
2. Description of the Prior Art
In the industrial manufacture of diverse types of apparata, such as, for example, watches, cameras, microscopes and the like, it is frequently necessary to adjust planar, frequently completely transparent, components relative to one another by machine, that is to say without human intervention. Thus, for example, when the planar components which are to be adjusted relative to one another are liquid-crystal displays, two small glass plates with optically transparent electrode structures applied thereto must be aligned relative to one another.
In some known liquid-crystal displays, for example, rectangular small glass plates having edge lengths of 10 to 30 mm are processed as the components which are to be adjusted. These plates having electrode patterns which have been vapour-deposited as a largely transparent layer and which have been etched, are to be made congruent to an accuracy of about 10 .mu.m. Since the accuracy of the break in the glass is insufficient, the electrode patterns are not in a defined position relative to the edge of the glass so that an adjustment to a limit stop cannot meet the set requirements. The almost transparent layers which serve as the electrodes are accessible to direct measurement techniques only with difficulty. For technological reasons, the provision of additional reference points, for example by imprints and the like, with a defined position relative to the geometry of the electrodes is impossible.
In the adjusting devices hitherto used, specially structured, etched zones are provided as marks on the small glass plates which are to be adjusted. The applied special structuring effects a local phase modulation of the light so that even completely transparent layers give a detectable signal in an optical dark field. Since the marks consist of parts of the same layer, from which the electrodes have also been produced, they have the same thickness as the electrodes. In the adjusting devices hitherto used, this fact does not yet raise particular problems since the components to be adjusted in this case are envisaged as glasses having electrode layer thicknesses of about 1,200 A.
For various reasons, such as price, invisibility and the like, electrode layer thicknesses of about 300 A are specifically desired in the construction of electro-optical displays, such as say liquid-crystal displays, so that serious problems arise, which cannot be solved with the adjusting devices hitherto used. Since the optical phase variation is then smaller by a factor of 4, the intensity available for the detection of the marks is reduced by a factor of about 20, and this gives an unsatisfactory signal/noise ratio in the adjusting devices hitherto used.